Don't waste your time. The "Cool Day/Night toggle swicth [sic]" will render text in your sidebar unreadable. Many of the other options remove legitimate features from YouTube videos. The UI is terrible. Could not uninstall quickly enough.

I have to echo similar sentiment with saying that using YouTube without Magic Actions isn't a world I want to live in.

Magic Actions lets you tweak just the right stuff so that every time you go to YouTube you are in the environment you want. Colors, activity, aspect ratio, quality, and the list goes on so when I want to watch some videos it is a consistent experience every time.